Automotive wheel speed sensor assembly with rotor and stator, one of which has only a few poles

ABSTRACT

There is described a speed sensor that is particularly adaptable to moving vehicles such as automobiles. A permanent magnet, stator assembly, and field coil are held within a ferromagnetic cup that is adapted to mate a bearing assembly of a non-driven wheel of the vehicle. A rotor assembly is carried by the wheel spindle. The rotor assembly has poles spaced entirely around the circumference of a circle while the stator assembly has only a few poles distributed over an arc of a portion of a circle. A magnetic flux is provided by the permanent magnet, which flux passes through the stator poles and the rotor poles. The ferromagnetic cup completes a flux path between the stator and rotor poles, and also to the magnet. The rotor poles rotate with the wheel, causing a changing magnetic flux which in turn generates an alternating voltage current in the field coil. The alternating current so generated is then fed through an electrical terminal to a vehicle computer.

BACKGROUND OF THE INVENTION

This application is a division of application Ser. No. 07/171,162 filedMar. 21, 1988, which itself is a continuation of application Ser. No.6/835,514 filed Mar. 3, 1986, now abandoned.

The present invention relates to a speed sensor and more particularly toa speed sensor that is particularly useful in braking systems ofvehicles such as automobiles.

Magnetic type induction speed sensors have been used to measure thespeed of rotating members for some years. However, when used inautomobiles, for example, the systems were attached externally to thewheel bearing assembly and were exposed to the environment. This isespecially hazardous when it is considered that the vehicle travels overall types of roadways.

The present invention represents an improvement over such prior artsystems in that the speed sensor functions within a grease cup of theautomobile's wheel bearing assembly.

SUMMARY OF THE INVENTION

Accordingly there is provided a speed sensor that is particularlyadaptable to vehicle braking systems which in general comprises a cup,an open end of which is adapted to mate a wheel bearing assembly of avehicle; a permanent magnet, a stator assembly, and a field coil allcarried in said cup; and electrical terminals electrically coupled tosaid field coil and extending outside said cup.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a speed sensor assembly employing thefeatures of the invention.

FIG. 2 is a partial section of the speed sensor of FIG. 1.

FIG. 3 is a partial section of another embodiment of a speed sensorassembly.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 and 2, there is shown a speed sensor assembly10 that is contained within a grease cup 12 of a wheel bearing assembly14 of an automobile. In general, wheel bearing assembly 14 includes aspindle 16 that rotates within housing 18 through bearings 19. Anautomobile wheel (not shown) is carried on spindle 16 to be rotated withthe spindle. Normally, the speed sensor assembly will be located on aspindle assembly of a wheel that is not driven by the automobile engine.Grease cup 12 is fabricated of steel in order to provide good fluxthrough the cup.

A plurality of rotor poles 22 extend from a rotor ring 17 which is pressfitted onto spindle 16 through flange 24 which is also press fitted ontothe spindle. The rotor ring as well as the poles are fabricated of steelor sintered iron in order to provide a good magnetic flux path.

Speed sensor assembly 10 includes a stator pole piece 26, a field coil28, and a permanent magnet 30. Stator pole piece 26 is fabricated fromsteel or sintered iron and includes a plurality of poles 32 of the samepolarity that extend over an arc of a portion of a circle and through aslot 42 of plate 38 to be in working relation to rotor poles 22.Permanent magnet 30 is fabricated of a barium ferrite or similar magnetmaterial. Field coil 28 is carried on a coil bobbin 33 in an annularspace 34. The bobbin has a central aperture 36 in which the stator polepiece 26 is substantially carried. Here, "substantially carried" meansthe structure as shown in FIG. 2 in which the major portion of statorpole piece 26 is contained within the aperture 36. The whole assembly isheld together through plate 38 and rivet 40.

An electrical connector 44 is attached to grease cup 12 and carries twoelectrical terminals 46 which engage bobbin 33. As shown, the terminalsare bent over at a right angle to create a compact assembly. Theterminal is held in place by ring 48 which is connected to cup 12 insealing relation through O-ring 50.

In operation, a magnetic flux path is created around the grease cup 12and the rotor ring 17 and through stator 26 by the permanent magnet 30when the rotor and stator poles are aligned. When rotor poles 22 arerotated simultaneously with the rotation of spindle 16, the magneticflux in the gap between the rotor poles 22 and stator poles 32 changesin intensity as the rotor moves from tooth to tooth of the stator poles.That is, upon misalignment of the rotor and stator poles, the fluxsweeps through field coil 28 to a position around an edge of permanentmagnet 30 causing a change in flux at the gap. This changing intensityin combination with the flux sweep causes an alternating voltage to begenerated in field coil 28 in which is then fed to a computer throughelectrical terminals 46. The use of a few stator poles as opposed to asingle pole or poles extending around a complete circle provides thestrongest magnetic pulsations and optimum generation of AC voltage incoil 28.

In addition, both the stator poles and rotor poles are tapered towardtheir tips such that the tip is less in thickness than the space betweenindividual teeth. This also increases the concentration of the magneticflux generated at the poles.

Another embodiment of the invention is shown in FIG. 3. In thisembodiment, the rotor poles are made part of the speed sensor assemblythat is contained within grease cup 90. Thus as shown, speed sensorassembly includes a stator cup 104 having an open end, a permanentmagnet 100 carried on a rotatable hub 102, field coil 106 carried inbobbin 108, and rotor poles 110. Stator poles 112 are attached to astator cup 104. They interact magnetically with rotor poles 110. A coverplate 114 closes the open end of the stator cup. Hub 102 rotates inbushings 116 and 118.

Hub 102 is mechanically coupled to spindle 16 through a bar or plate 120that is fixed to the hub and a pin 122 that is carried by the spindlethrough flange 124. Rotation of spindle 16 causes engagement of pin 122with bar 120 to rotate hub 102 and thus permanent magnet 100 and rotorpoles 110. Rotation of the rotor poles causes an alternating current tobe induced in field coil 106 in the same manner as that with respect tothe embodiment of FIGS. 1 and 2.

What is claimed is:
 1. In a speed sensor assembly for providing anelectrical signal representative of the speed of an automotive vehiclewheel, said assembly of the type including rotor means for providing oneor more poles that rotate with said wheel, stator means for providingone or more poles that do not rotate with said wheel, magnetic means forgenerating magnetic flux through said one or more rotor poles and saidone or more stator poles, means for supporting said rotor means, saidstator means and said magnetic means so that as said wheel turns saidone or more rotor poles are at times aligned with said one or morestator poles and at other times are not aligned with said one or morestator poles, and field coil means for interacting with said magneticflux to generate said electrical signal in response to changes in saidflux caused by said one or more rotor poles moving with respect to saidone or more stator poles when said wheel moves, the improvement wherein:one of said rotor means and said stator means has no more than a fewpoles, and the other of said rotor means and said stator means has polesspaced substantially entirely around the circumference of a circle; andsaid magnetic means includes ferromagnetic means for causing saidmagnetic flux to sweep through said field coil means when said one ormore rotor poles move from a position in which they are aligned withsaid one or more stator poles to a position in which they are not soaligned.
 2. A speed sensor assembly as in claim 1 wherein said no morethan a few poles are distributed over an arc of a portion of a circle.3. The combination of vehicle wheel speed sensor with a vehicle wheelbearing assembly, said combination comprising:a wheel bearing housing; awheel bearing spindle rotatable in said wheel bearing housing; rotormeans for providing one or more poles that rotate with said spindle;stator means for providing one or more poles that do not rotate withsaid spindle; magnetic means for generating magnetic flux through saidone or more rotor poles and said one or more stator poles; means forsupporting said rotor means, said stator means and said magnetic meanson said wheel bearing assembly so that as said wheel turns said one ormore rotor poles are at times aligned with said one or more stator polesand at other times are not aligned with said one or more stator poles;and field coil means for interacting with said magnetic flux to generatesaid electrical signal in response to changes in said flux caused bysaid one or more rotor poles moving with respect to said one or morestator poles when said wheel spindle rotates; wherein one of said rotormeans and said stator means has no more than a few poles, and the otherof said rotor means and said stator means has poles spaced substantiallyentirely around the circumference of a circle; and said magnetic meansincludes ferromagnetic means for causing said magnetic flux to sweepthrough said field coil means when said one or more rotor poles movefrom a position in which they are aligned with said one or more statorpoles to a position in which they are not so aligned.
 4. A combinationas in claim 3 wherein said no more than a few poles are distributed overan arc of a portion of a circle.
 5. The combination as in claim 3wherein said magnetic means further includes a magnet and saidferromagnetic means comprises a ferromagnetic member extendingsubstantially from said rotor means to said magnet whereby a flux pathpassing from said magnet through said stator means to said rotor meansand through said ferromagnetic member back to said magnet encircles saidcoil.